1. Field of the Invention
This invention generally relates to a continuous web printing press and specifically such continuous web printing presses with page cutting apparatus.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R 1.97-1.99
Continuous web printing presses, such as high speed, high volume rotary presses such as used to print newspapers and the like, generally have a plurality of paper webs. These plurality of webs from a plurality of separate printing units are sent via separate paths to a single folding/cutting mechanism. Each printing unit has at least one plate cylinder and at least one blanket cylinder for printing on the web. Each printing unit also has numerous other running cylinders and rollers for threading the web through the printing unit and to the folding/cutting mechanism for cutting into detached pages. It is necessary that the cutter of the folding/cutting mechanism cut the webs at the imaginary page boundary lines between the adjacent pages as printed on the web. In known rotary printing presses, the cutter is stationary with respect to the cylinders that print the image on each web, and proper cut-off registration is achieved by adjusting each web path length. It is well known for press operators to manually adjust the web path length based upon their visual observation of the cut paper product as it comes out of the folding/cutting mechanism. It is also well known that once the web path adjuster is set for a given cut-off registration, there are other variables which can cause improper registration which must be corrected by resetting the web path adjuster. A change in press speed generally requires an adjustment to maintain proper cut-off registration. In addition, a change in paper is known to require an adjustment due to a change in moisture content or elasticity of the paper.
Apparatus for achieving proper page cutting registration are also well known. These methods use photosensors that detect the location of printed pages on the webs by optically detecting either the edges of the normal printing array or by detecting special reference marks printed on the page using the same ink as is used to print the printed body of the page. An example of a control apparatus that optically detects the printed body of the page is described in U.S. Pat. No. 4,896,605 issued Jan. 30, 1990 to Schroder. A disadvantage of this method is that the printing press must print the entire printed body of the page before detection and registration can be obtained. In addition, optical detection of printing requires that the printing be clear. Other known methods merely maintain, but cannot initially establish, cut-off registration as shown in U.S. patent application Ser. No. 787,491 filed on Nov. 4, 1991 of Hudyma et al. Disadvantageously, pages printed by a rotary printing press immediately after it starts, or during starting, are not sufficiently clear to enable reliable photoptical detection. Accordingly, these methods that depend upon optically detecting the normal printed body of the page image or detecting special reference marks printed by the same means used in normal printing are unable to achieve proper registration quickly. Accordingly, there is a wastage of ink, paper and other resources as well as a disposal problem due to production of improperly cut pages.
Examples of devices in which reference marks are printed on the web by means separate from the main printing mechanism are shown in U.S. Pat. No. 5,088,403 issued Feb. 18, 1992 to Shoji and U.S. Pat. No. 5,119,725 issued Jun. 9, 1992 to Okamura. However, poor printing quality of the newspaper image such as occurs when a press is starting can obliterate the independently printed reference marks, thereby delaying the determination of proper cut-off registration.
Furthermore, these methods suffer from other disadvantages. The presence of ink, dirt, dust or oil in a printing press environment are common and can significantly interfere with the ability of the photosensors to operate properly and these devices therefore require frequent cleaning. Precise alignment between the relatively small reference mark and the sensor is necessary for proper detection but difficult to obtain and to maintain during press operation. This alignment problem is partially difficult to solve due to sideways web drift which is inherent in rotary printing presses. In addition, known methods which use separate devices to print reference marks disadvantageously require complicated blanket cylinder phase detection device to print the reference marks in phase with the blanket cylinder which are prone to failure if not properly installed and maintained.
Another disadvantage of known optical or photoelectric based page cut controllers is that a separate sensor is required for each web since the opacity of the paper makes it impossible to detect marks on one web through the body of another web or through the body of the one web.
With known page cutting controllers, it is not possible to place a plurality of sensors in close proximity to the folding/cutting mechanism due to a lack of space between the webs at the entry point to the folding/cutting mechanism. Specifically, it has not been possible to place a plurality of sensors as close as one page length away from the cut. The most accurate determination of registration is achieved when the sensors are placed as close as possible to the cutter, so the inability to place a plurality of sensors near the folding/cutting mechanism significantly detracts from accuracy.